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Heteroanionic tuning of electronic and optical properties in cobaltite oxide films
Dissertation   Open access

Heteroanionic tuning of electronic and optical properties in cobaltite oxide films

Tessa Dae Tucker
Doctor of Philosophy (Ph.D.), Drexel University
Jun 2026
DOI:
https://doi.org/10.17918/00011473
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Abstract

Cobaltite oxides are scientifically and technologically attractive materials for their structural versatility and property tunability. This tunability can be further expanded by topotactically manipulating the oxygen content or incorporating a second anion, such as F⁻, to alter the metal-anion bond ionicity or the metal charge density, leading to changes in functional properties such as optical absorption or electron transport. For my dissertation, I utilize both topochemical and electrolytic biasing-based insertion of anions into cobaltite oxide films to alter their structural, electronic, and optical properties. I demonstrate a blue-shift of the optical absorption edge in SrCo(O,F)_[3-x] films upon fluoride incorporation, a result that reveals a distinct strain-dependence to optical absorption in oxyfluorides that runs in contrast to that observed in their oxide counterparts. The second half of this dissertation, I focus on Ruddlesden-Popper (RP) cobaltites. I use molecular beam epitaxy to synthesize RP Sr_[n+1]Co_nO_[(3n+1)-[delta]] (n = 1 and 2) thin films using a brownmillerite SrCoO_[2.5] capping layer, revealing the strong role that substrate selection plays in phase stability. Last, I show that LaSrCoO_[4-[delta]] cobaltites exhibit significantly improved stability compared to Sr₂CoO_[4-[delta]], allowing for electrolytic oxidation and reduction of RP films and thus voltage control of physical properties.

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